// This file is part of Substrate.

// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use sp_core::U256;

pub trait Bits {
	/// Arithmetic shift right by `rhs` bits.
	#[must_use]
	fn arithmetic_shr(self, rhs: usize) -> Self;
}

impl Bits for U256 {
	fn arithmetic_shr(self, rhs: usize) -> Self {
		const BITS: usize = 256;
		let sign = self.bit(BITS - 1);
		let mut r = self >> rhs;
		if sign {
			r |= U256::MAX << BITS.saturating_sub(rhs);
		}
		r
	}
}

#[cfg(test)]
mod tests {
	use super::*;
	use proptest::proptest;

	#[test]
	fn test_arithmetic_shr() {
		proptest!(|(limbs: [u64; 4], shift in 0usize..=258)| {
			let ours = U256(limbs).arithmetic_shr(shift);
			let theirs = alloy_core::primitives::U256::from_limbs(limbs).arithmetic_shr(shift);
			assert_eq!(&ours.0, theirs.as_limbs());
		});
	}
}
